1. Field of the Invention
The present invention relates to a method of fabricating a polymer optical circuit.
2. Description of the Related Art
The following have been proposed as methods of fabricating a polymer optical circuit: (1) a method of impregnating a film with a monomer, selectively exposing a core portion so as to change the refractive index, and laminating films together (a selective polymerization method); (2) a method of coating a core layer and a clad layer, and thereafter, forming a clad portion by using reactive ion etching (RIE method); (3) a method using photolithography which carries out exposure and development by using an ultraviolet curable resin which is obtained by adding a photosensitive material into a polymer material (a direct exposure method); (4) a method using injection molding; (5) a method of coating a core layer and a clad layer, and thereafter, exposing a core portion so as to change the refractive index of the core portion (a photobleaching method); and the like.
Thereamong, attention has focused on the following method as a method by which a polymer optical circuit having little transmission loss of the waveguide core can be fabricated: a film for a clad is firmly stuck to the surface at the side where a concavity is formed at a silicone rubber mold in which the concavity corresponding to the pattern of the waveguide core is formed, and a resin for waveguide core formation is injected into the concavity and cured so as to form the waveguide core at the surface of the film for the clad (Japanese Patent Applications Laid-Open Nos. 2004-086144, 2004-109926).
It is often the case that polymer optical circuits are made able to be connected to light emitting/receiving elements by forming an inclined mirror having an approximately 45° angle with respect to the optical axis of the waveguide core, or by forming a convex lens, at the final end of the waveguide core. The inclined mirror has an angle of about 30° to 60°, and functions to couple, to the waveguide core, light which propagates in the normal direction of the surface at which the waveguide pattern is formed. Accordingly, the angle of a usual inclined mirror is formed to be 45°.
In polymer optical circuits fabricated by the methods disclosed in aforementioned JP-A Nos. 2004-086144 and 2004-109926, an inclined mirror can be formed by cutting the final end of the waveguide core by a dicing saw having a dicing blade whose distal end is substantially V-shaped.
However, when an inclined mirror is formed at the final end portion of a waveguide core, the surface roughness of the inclined mirror must be made to be less than or equal to 1/10 of the wavelength of the light which propagates through the waveguide core. Accordingly, when the inclined mirror is to be finished by a dicing saw, precision cutting by the dicing saw must be carried out, and polishing processing must be carried out separately if necessary.
Here, in a cutting process by a dicing saw, the processing time is determined in accordance with the feed speed of the dicing blade. When a 45° surface is to be finished by a dicing saw, the feed speed of the dicing blade cannot be set to be high, and therefore, a long time is required for the processing. Further, when an inclined mirror is to be formed at a waveguide core, a dicing blade for a 45° surface and a dicing blade for cutting-off perpendicularly are separately required, and retooling becomes complex.
Further, at a dicing saw, the optical path changing direction of an inclined mirror can only be made to be the direction in which the dicing saw has an attracting surface. Therefore, when forming an inclined mirror at the final end of a waveguide core at a polymer optical circuit, there is the need to machine one final end first, and then, after peeling the polymer optical circuit off from a dicing tape and reversing the front and back thereof, again affix it to a dicing tape and machine the other final end. Accordingly, if inclined mirrors are to be formed at the both end portions of a polymer optical circuit, as compared with a case in which an inclined mirror is to be formed at only one end portion, the number of processes increases, and further, the amount of the dicing tape which is used doubles. Moreover, there is also the possibility that the positional relationship between the two inclined mirrors will be disturbed due to an error in the affixing position at the time when the polymer optical circuit is affixed to the dicing tape the second time.
Thus, the following methods have been proposed as methods of shaping a final end of a waveguide core without using a dicing saw: a method of placing an optical waveguide at a die and forming the inclined mirror by punching by a punch (JP-A No. 2006-011179); a method of injecting a core material into a mold of a predetermined shape and curing the core material so as to form a waveguide core having inclined mirrors at the both ends, and forming a convex lens for light collection by stamping by a mold at the clad layer which surrounds the waveguide core (JP-A No. 2005-181645); a method of forming a waveguide core by photolithography, wherein an inclined mirror is formed by changing the exposure conditions of a waveguide core end portion (JP-A No. 2000-298221); a method of forming a waveguide core by using a silicone rubber mold, wherein portions corresponding to inclined mirrors are formed at both ends of the silicone rubber mold (JP-A No. 2004-078084); and the like.